Fluid management system

ABSTRACT

A fluid management system with a detection circuit for detecting whether an attached surgical device is operational. The fluid management system changes at least one operation mode when the surgical device is detected as being operational. The fluid management system may include inflow, outflow, or inflow/outflow capabilities, and monitors at least one signal characteristic of an AC power signal provided to the surgical device.

This is a divisional of application Ser. No. 12/562,881, filed Sep. 18,2009, now U.S. Pat. No. 8,206,342, which claims the benefit of U.S.Provisional Application No. 61/136,628, filed Sep. 19, 2008, theentirety of which is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a system for managing fluid inflowand/or outflow to an operative site (e.g., a knee joint), while alsodetecting whether a surgical device (such as a shaver) connected to thesystem is in an operational state.

2. Description of the Related Art

During arthroscopic surgery, it is necessary to have a clear field ofvision, which requires reduction of blood flow into the operative site,quick removal of debris, and distension of joint spaces sufficient tomaneuver surgical instruments. Fluids introduced under pressure into theoperative site achieve these objectives. One such prior art fluidmanagement system is the arthroscopy infusion pump described in U.S.Pat. No. 5,520,638, assigned to Arthrex, Inc., the disclosure of whichis incorporated by reference in its entirety.

Prior art fluid management systems typically utilize one tube to deliverfluid under pressure to the operative site, a second tube to remove thefluid from the operative site while the surgical device is not beingoperated, and a third tube to remove the fluid from the operative sitewhile the surgical device is being operated. That is, the fluid entersthe operative site through the first tube and exits the operative sitethrough one of the second or third tubes. Both the second and thirdtubes are simultaneously connected to the operative site. When thesurgical device is not being operated (e.g., when a shaver trigger on ashaver is not depressed), the fluid exits the operative site through thesecond tube, referred to as a “cannula tube.” When the surgical deviceis being operated (e.g., when the shaver trigger is depressed), then thefluid exits the operative site through the third tube, referred to as a“device tube” (or, when the surgical device is a shaver, a “shavertube”).

In some conventional fluid management systems that are configured foruse with a particular surgical device, switching of the outflow path isdesigned to occur automatically with operation of the surgical device.When a particular surgical device is designed for use with a particularfluid management system, the controls of the two may simply beintegrated to provide this feature. Surgical devices from many differentmanufacturers and with many different part numbers, however, may be usedin conjunction with such fluid management systems. In fact, it is commonfor a surgeon to have a preferred surgical device—such as a preferredshaver console and/or hand piece—that may or may not be the samemanufacturer as that of the fluid management system. It is also commonfor a surgical device from one manufacturer to be used with a fluidmanagement system from another manufacturer. In such situations,compatibility problems can arise. For example, the fluid managementsystem of one manufacturer is not able to detect when an attachedsurgical device from another manufacturer is being operated. Thus, thefluid management system may not be capable of automatically switchingbetween the cannula tube and the device tube for outflow from theoperative site, without the use of a customized detection device.

For example, one such prior art fluid management system that includes adetection device is the FMS Duo manufactured by DePuy Mitek, and asdescribed in U.S. Pat. Nos. 4,902,277, 5,000,733 and 5,131,823, thecontents of which are incorporated herein by reference. The FMS Duoutilizes a shaver detection device that is specific to each shaver handpiece cord. The shaver detection device has a male/female connector thatmust be custom made for each shaver hand piece model on the market.Thus, when a new shaver hand piece is developed by a given manufacturer,a new shaver detection device must also be developed by DePuy Mitek inorder to properly operate the fluid management system for its intendedpurpose.

Accordingly, there exists a need in the art for an improved fluidmanagement system which does not require a separate custom-madedetection device for each surgical device on the market.

Also in conventional fluid management systems, switching between theoperational and non-operational outflow fluid pathways (i.e., thecannula and device tubes) is physically accomplished by a pinchmechanism, commonly including a rotating wheel located between the twotubes. The wheel is configured to switch between restricting—or“pinching off”—one of the two tubes, while allowing fluid to travelthrough the other. This configuration results in a complicated procedurefor connecting the tubes to the fluid management system. For example,conventional pumps require that the user install one outflow tube first,press a pinch button to move the pinch mechanism, and then load thesecond outflow tube.

Accordingly, there exists a need in the art for an improved fluidmanagement system and method for easing installation and replacement ofoutflow tubes.

The pressure at which fluids are introduced at an operative site ispreferably stable over a period of time, and capable of being specifieddepending upon the use. Prior art systems include pressure sensors todetect an inflow pressure at the operative site, but this requiresadditional intrusive components at the operative site. The pressure caninstead be estimated based upon the pressure at the output of an inflowpathway of an inflow/outflow pump. However, these inflow pressureestimates can be inaccurate, especially when a surgical device isoperational at the operative site.

Accordingly, there exists a need in the art for improved devices andmethods for compensating for variations in pressure levels at theoperative site.

SUMMARY OF THE INVENTION

The present invention fulfills the needs noted above by providing afluid management system with a detection circuit that monitors signalcharacteristics of an AC power signal provided to an attached surgicaldevice to detect when the surgical device is being operated (i.e., whenthe device is operational). In one embodiment, the surgical device is ashaver, and the fluid management system is an inflow/outflow pump. Whenthe fluid management system detects that the surgical device is beingoperated, it can automatically adjust operation modes accordingly. Forexample, when the detection device described herein detects that thedevice is operational, the fluid management system can switch theoutflow path to an operational outflow path, and also increase the fluidflow rate and/or pressure to help eject debris that may be generatedduring use of the surgical device. When the fluid management systemdetects that the surgical device is no longer being operated, the fluidmanagement system again adjust operation modes—i.e., switches theoutflow back to the non-operational outflow path and the flow rateand/or pressure back to the non-operational rate.

The detection circuit is coupled between the power cord of the surgicaldevice and an interface for an AC power cord on the fluid managementsystem. The detection circuit detects a change between a non-operationallevel of one or more signal characteristics (i.e., when the surgicaldevice is not being operated) and operational level of the signalcharacteristics (i.e., when the surgical device is being operated). Thefluid management system can utilize a standard IEC 320 connector thatconnects to the power receptacle or power cord of many conventionalsurgical devices, such as the console of most shaver devices; thus thereis no need for a customized detection device for every brand orvariation of surgical device on the market. The fluid management systemmay also be programmed to detect the manufacturer and part numberattached thereto based upon the current load measured during theoperational state.

A rotating motor can be used to operate a wheel configured to switch theoutflow fluid path between the non-operational path (i.e., a cannulatube) to the operational path (i.e., a device tube). The rotating motormay be, for example, a stepper motor, providing precise rotation. Therotating motor can be configured to rotate to the center of its axisduring loading and unloading of the outflow tubes, rather than beingaligned to pinch off one of the outflow tubes. This design improvesloading of the tubes, and allows for use of a detachable cassetteholding the tubes.

The fluid management system can also be configured to estimate the fluidpressure at the operative site, and may utilize a pressure algorithm toestimate the pressure based upon the operational flow rate. The pressurealgorithm may estimate the pressure without the need for taking anactual pressure measurement at the operative site. This eliminates theneed for an additional incision for a pressure monitor as required byprior art fluid management systems, while also compensating for varyingconditions at the operative site. The pressure algorithm can be adjustedaccording to the operational state as well as the inflow and/or outflowrate of the fluid management system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a fluid management system andconnected surgical device, in accordance with an exemplary embodiment ofthe invention;

FIG. 2A illustrates a block diagram of the detection circuit of thefluid management system of FIG. 1, in accordance with an exemplaryembodiment of the invention;

FIG. 2B illustrates a block diagram of the detection circuit of thefluid management system of FIG. 1, in accordance with another exemplaryembodiment of the invention;

FIG. 3 illustrates a block diagram of the pump control circuit of thefluid management system of FIG. 1, in accordance with an exemplaryembodiment of the invention;

FIG. 4 illustrates a flow diagram of a method for controlling the fluidmanagement system of FIG. 1, in accordance with an exemplary embodimentof the invention;

FIG. 5 illustrates a flow diagram of a method for controlling anotheraspect of the fluid management system of FIG. 1, in accordance with anexemplary embodiment of the invention;

FIG. 6 illustrates a front view of a fluid management system, inaccordance with an exemplary embodiment of the invention;

FIG. 7 illustrates a close-up front view of a fluid management system,in accordance with an exemplary embodiment of the invention; and

FIG. 8 illustrates an exploded view of a fluid management system, inaccordance with an exemplary embodiment of the invention;

FIG. 9 illustrates a front view and a cross-sectional view of a cassettefor a fluid management system, in accordance with an exemplaryembodiment of the invention;

FIG. 10 illustrates an exploded rear view of a section of a fluidmanagement system, in accordance with an exemplary embodiment of theinvention;

FIG. 11 illustrates a flow diagram of a method for controlling anotheraspect of a fluid management system, in accordance with an exemplaryembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a fluid management system with adetection circuit and methods for controlling the same. Referring now tothe drawings, where like elements are designated by like referencenumerals, FIGS. 1-11 illustrate the apparatus and methods of the presentinvention.

Referring to FIG. 1, a fluid management system 100 is illustrated, inaccordance with an exemplary embodiment of the invention. In onepreferred embodiment, fluid management system 100 is operationallysimilar to the Continuous Wave III Arthroscopy Pump (Part No. AR-6475),as manufactured by Arthrex, Inc., and also similar to the arthroscopyinfusion pump described in U.S. Pat. No. 5,520,638. However, fluidmanagement system 100 includes additional features, some of which aredescribed further below, that are not found in the prior art.

Fluid management system 100 provides fluids under pressure to anoperative site, and/or removes fluids and other materials from theoperative site, such as via an inflow pump for providing fluid underpressure to an operative site, an outflow pump for removing fluid fromthe operative site, or an inflow/outflow pump. Fluid management system100 may provide both inflow and outflow fluid management simultaneously,but need not include both functions.

If configured to provide outflow operations, fluid management system 100includes at least an operational path (i.e., the device tube) and anon-operational path (i.e., the cannula tube). If configured to provideinflow operations, fluid management system 100 includes an inflowpathway to provide fluid at a relatively stable flow rate. Suction atthe outflow pathway and pressure at the inflow pathway can be providedand controlled by, for example, variable-speed peristaltic motors, asare known in the art. The inflow and/or outflow pump components of fluidmanagement system 100 receive power via power cord 130.

Fluid management system 100 is coupled to a surgical device. Thesurgical device may include a hand piece 110 coupled to a device console105; for example, a shaver hand piece and shaver console, respectively,as is known in the art. It should also be understood that a surgicaldevice for use with embodiments of the fluid management system describedherein need not include a console and hand piece, but may be anysurgical device known in the art that has controllable operation and isdesirable for use with a fluid management system.

The console 105 of the surgical device is coupled to the fluidmanagement system by power cord 140, which acts as a conduit for an ACsignal to the surgical device. Power cord 140 may be any known powercord for surgical devices, and may be a standard power cord such as anIEC 320 power cord, as is known in the art. When the surgical device isnot being operated (e.g., when a trigger on hand piece 110 is notdepressed), an AC signal having first signal characteristics (i.e., asteady state signal) is supplied to console 105 via power cord 140.However, when the surgical device is being operated (e.g., when thetrigger is depressed), then an AC signal having different signalcharacteristics (i.e., typically including signal characteristic withincreased levels than the steady state levels) is supplied to console105 via power cord 140.

Fluid management system 100 conducts operations—such as inflow, outflow,and/or pressure estimation—according to operation modes such as, but notlimited to, inflow pressure, inflow flow rate, outflow flow rate,outflow fluid path, and pressure algorithm. One or more of theoperational modes are desirably adjusted when an attached surgicaldevice is in an operational state versus a non-operational state.

Fluid management system 100 also includes a detection circuit 115.Detection circuit 115 is isolated (indicated by element 135), andpreferably galvanically isolated, from other circuitry within fluidmanagement system 100 so as to not compromise the electric measurementsbeing taken. Detection circuit 115 can be located integral to the samestructure as the inflow/outflow pump components of fluid managementsystem 100, or may be located external to this structure, for example onan external board. Power can be provided to detection circuit 115 by aseparate power cord 125, or from the inflow/outflow pump via an internalconnection or a second power cord.

Detection circuit 115 detects changes in the operational status of theattached surgical device by detecting changes in the power provided tothe surgical device via cord 140. Detection circuit 115 monitors levelsof one or more signal characteristics of the AC signal provided to powercord 140, including, but not limited to, current, voltage, noise level,and/or power. Because detection circuit 115 is provided as part of fluidmanagement system 100 rather than in power cord 140, detection circuit115 does not rely on the power cord of the surgical device, and candetect changes in operational status of various connected surgicaldevices by different manufacturers.

Fluid management system 100 can automatically change or adjust variousoperation modes according to the detection. For example, when detectioncircuit 115 detects that the surgical device is not being operated, itcan provide a signal to pump control circuit 120 to control the outflowso that the fluid exits the operative site from the non-operational path(i.e., the cannula tubing) and also controls the inflow and outflowrates to be non-operational flow rates. When detection circuit 115detects that the surgical device is being operated, it can provide asignal to pump control circuit 120 to control the outflow so that thefluid exits the operative site from the operational path (i.e., theshaver tubing) and also increases the inflow and outflow rates to bepre-set operational flow rates. Other operation modes, including inflowpressure and a pressure algorithm used to estimate pressure at theoperative site, can also be adjusted or changed accordingly.

FIG. 2A illustrates a block diagram of detection circuit 115 of FIG. 1,in accordance with one exemplary embodiment of the invention. Detectioncircuit 115 includes a current measurement circuit 205 that monitors thechange in current load being supplied to the surgical device. AC powerthat is used by the surgical device (i.e., at console 105 of FIG. 1) ismeasured by current measurement circuit 205. Current measurement circuit205 is electrically isolated from the inflow/outflow pump components offluid management system 100, and galvanically isolates the currentprovided to power cord 140.

When the surgical device is not being operated, a non-operationalcurrent level being supplied to console 105 is measured by detectioncircuit 115. However, when the surgical device is being operated, ahigher level of current (i.e., higher than the non-operational currentlevel) is measured by detection circuit 115 as being supplied to theshaver console 105.

FIG. 2A also depicts power supply 240. Power supply 240 may receivepower via separate power cord 125, or from the inflow/outflow pump powersupply 130. In one embodiment, detection circuit 115 is separate andexternal to the inflow/outflow pump components of fluid managementsystem 100, and power supply 240 receives power via separate power cord125. In another embodiment, detection circuit 115 is internal to theinflow/outflow pump components of fluid management system 100, andreceives power from the DC supply used to power circuitry of theinflow-outflow pump components, such as pump control circuit 120 (FIG.1).

In either case, current measurement circuit 205 is preferablyelectrically isolated from DC power supply 240 to prevent interferencewith the detected current being provided to the surgical device. Forexample power supply 240 may include DC-to-DC converters acting asisolating voltage regulators to galvanically isolate power provided fromthe DC supply used to power circuitry of the inflow-outflow pumpcomponents. Power supply 240 may also include a transformer togalvanically isolate power provided by a separate source (i.e., separatepower cord 125), or to further galvanically isolate power providedinternally. In accordance with one embodiment, when detection circuit115 is external to the inflow/outflow pump components of fluidmanagement system 100, the transformer decouples the detection circuit'sDC signals from the power supply of the surgical device, and is where DCsupply signals for detection circuit 115 are generated, rectified, andprovided to the components.

Power cord 140, which provides power to the attached surgical device(FIG. 1), is coupled to current measurement circuit 205. Detectioncircuit 115 continually monitors the surgical device's currentconsumption. Current measurement circuit 205 (either constantly orrepeatedly) generates a signal according to the amount of currentprovided to power cord 140. For example, when an attached surgicaldevice is operational (i.e., hand piece 110 of FIG. 1 is turned on),current consumption by the surgical device (i.e., from power cord 140 toconsole 105 of FIG. 1) increases in order to supply power for operation.The signal is fed by the current measurement circuit 205 through asignal conditioning circuit 210. Signal conditioning circuit 210generates a linear DC voltage between 0 and 5 volts representing theamplitude of the signal from the current measurement circuit 205, whichin turn represents the current consumption of the surgical device.Signal conditioning circuit 210 provides the linear DC voltage to aninput of signal control circuit 215, which can be, for example, amicro-controller. Signal control circuit's 215 input may also include ananalog-to-digital converter for converting the linear DC voltage to adigital voltage value. This digital voltage value may then be comparedto a baseline value to determine the operational status of the surgicaldevice, as well as to identify the manufacturer and/or part number ofthe surgical device, as further described below.

Signal control circuit 215 then generates an appropriate signal viacoupler 220. The signal is provided to pump control circuit 120 (seeFIG. 1), which controls the outflow and/or inflow operations of thefluid management system 100 according to whether the surgical device isbeing operated. (A separate signal identifying the surgical device mayalso be sent to pump control circuit 120, if so determined.) Coupler 220is configured to provide a signal between detection circuit 115 and pumpcontrol circuit 120 while maintaining electrical isolation between thetwo components.

Coupler 220 may be, for example, an optocoupler that produces a logicsignal, with an input that is electrically isolated from its output. Inone embodiment, signal control circuit 215 contains a logic pin that isnormally at ground, meaning that the input of coupler 220 is also atground. However, coupler 220 may use a logic “NOT,” resulting in theoutput of the coupler 220 being logic high (i.e., 5 volts DC). When thelogic pin of signal control circuit 215 switches to a logic high (i.e.,5 volts DC), indicating increased power being provided to the surgicaldevice, the output side of coupler 220 switches to logic low. The logicsignal from detection circuitry 115 is provided to pump control circuit120 (FIG. 1), described further below.

FIG. 2B illustrates a block diagram of a detection circuit in accordancewith another exemplary embodiment of the invention. Detection circuit115B shown in FIG. 2B is similar to detection circuit 115 shown in FIG.2A, and like reference numbers designate like elements. Detectioncircuit 115B, however, includes voltage measurement circuit 207 andsignal conditioning circuit 212, rather than, or in addition to, currentmeasurement circuit 205 and signal conditioning circuit 210 of FIG. 2A.In FIG. 2B, power cord 140, which provides power to the attachedsurgical device (FIG. 1), is coupled to voltage measurement circuit 207.Voltage measurement circuit 207 monitors the change in voltage at theinterface to power cord 140.

Although detection circuits 115 and 115B include current measurementcircuit 205 and voltage measurement circuit 207, respectively, detectioncircuit 115 may instead (or additionally) include circuits designed tomeasure other signal characteristics. For example, detection circuit 115may also include a noise measurement circuit designed to measure thenoise level of the AC signal provided to power cord 140. It should beunderstood that many known AC signal characteristics and correspondingcircuits for measuring these AC signal characteristics are known in theart, and any such circuit for measuring an AC signal characteristic maybe used with the detection circuit described above.

In addition, multiple signal characteristics may be measured fordetection. For example, it should also be noted that the accuracy ofdetection circuit 115 and/or 115B can be improved upon by monitoringboth the current provided to the surgical device and the power cordvoltage level. The power usage of the surgical devices can be calculatedby using both monitored current and voltage levels. By using thecalculated power, deviations in line voltage can be filtered out and,and false current surges can be eliminated.

When the surgical device is not being operated, a non-operationalvoltage level at the interface to power cord 140 is measured bydetection circuit 115. However, when the surgical device is beingoperated, a higher level of voltage (i.e., higher than thenon-operational voltage level) is measured by detection circuit 115 atthe interface to power cord 140. Signal conditioning circuit 212generates a linear DC voltage between 0 and 5 volts representing theamplitude of the signal from voltage measurement circuit 207, which inturn represents the voltage consumption of the surgical device.

FIG. 3 illustrates a block diagram of pump control circuit 120 of thefluid management system 100 (FIG. 1), in accordance with an exemplaryembodiment. The isolated signal from detection circuit 115 is providedthrough a detection circuit interface 310 to pump controller 300. Pumpcontroller 300, which may be a micro-controller, recognizes that thesignal went from 5 volts (indicating non-operational status of thesurgical device) to ground (indicating operational status). The pumpcontrol circuit 120 in turn switches the outflow of the inflow/outflowpump to the operational outflow path (i.e., the device tube), adjuststhe speed of the motors controlling pressure of the outflow and/orinflow tubes to increase or decrease the flow rate, adjusts the inflowpressure, adjusts a pressure algorithm (discussed further below) and/oradjusts other operation modes of fluid management system 100.

FIG. 4 illustrates a flow diagram of a method 600 for controlling thefluid management system 100 of FIG. 1, in accordance with an exemplaryembodiment. Although for purposes of clarity, method 600 showsmonitoring current levels, it should be understood that the steps ofmethod 600 could include monitoring other signal characteristics,instead of or in addition to, current level. For example, in steps 605,625, and 645, a voltage level at the interface of the fluid managementsystem 100 may be detected, rather than a current level. Alternatively,both voltage and current levels, or other signal characteristics, couldbe detected.

Method 600 begins at step 601. At step 605, signal characteristics suchas the current level being supplied to the surgical device are detectedby detection circuit 115 (FIG. 1), as described above. At step 610, adetermination is made whether the surgical device is being operated. Ifnot, the non-operational outflow path (i.e., the cannula tube) andnon-operational flow rates are maintained, as shown at step 615. If itis determined that the surgical device is being operated, however, theoutflow path is switched to the operational outflow path (i.e., thedevice tube) and the inflow and/or outflow rates also may be increasedto an operational level at step 620.

In addition, other operation modes of fluid management system 100 may bechanged accordingly at step 620. For example, as further describedbelow, a pressure algorithm for determining the pressure at theoperative site may also be adjusted accordingly. The pressure algorithmmay be adjusted by changing variables and factors within the algorithmknown to vary according to increases or decreases in inflow and/oroutflow rate, or by using different algorithms known to produce moreaccurate estimates at different flow rates according to the detectedoperational status of the surgical device and/or the detected flow rateset by pump control circuit 120.

Additionally, prior to switching the outflow path and inflow/outflowrates at step 620, the manufacturer and/or part number of the attachedsurgical device may be determined at step 700, and the identifiedsurgical device's optimal inflow/outflow rates set in the pump control,as further described below with regard to FIG. 5.

Returning to FIG. 4, at step 625, signal characteristics (such ascurrent level) are again detected, and at step 630, a determination ismade as to whether the surgical device remains in an operational state.If so, the operational outflow path and flow rates are maintained, asshown at step 635, and the determination of step 630 is made again aftera predetermined amount of time. If the operational status has changed(i.e., the shaver is detected as being non-operational), then at step640, the outflow path is switched to the non-operational path (i.e., thecannula tube), the inflow and/or outflow rates are decreased to thenon-operational flow rate, and/or other operation modes are adjustedaccordingly.

At steps 645 and 650, signal characteristics are again detected and adetermination is made whether the surgical device has switched to anoperational state. If not, the non-operational operation modes aremaintained, and the determination is made again after a predeterminedtime. If the operational status has changed (i.e., the shaver isdetected as being non-operational), then the flow diagram returns tostep 620. Alternatively, the flow diagram may return to step 700(identifying the attached surgical device).

FIG. 5 illustrates a flow diagram of a method 700 for identifying thesurgical device attached to the fluid management system 100 of FIG. 1,in accordance with another exemplary embodiment. Although for purposesof clarity, method 700 shows monitoring current levels, it should beunderstood that the steps of method 700 and discussed below couldinclude monitoring other signal characteristics, instead of or inaddition to, current level. For example, in steps 710 and 720, a voltagelevel at the interface of the fluid management system 100 and a voltagedifferential may be detected, rather than a current level.Alternatively, both voltage and current levels, or other signalcharacteristics, could be detected.

The method begins at step 705, which, as discussed above, occurs afterstep 610 and prior to step 620 of FIG. 4. At step 710, operationalsignal characteristic levels—such as the level of operational currentbeing supplied via power cord 140 (FIG. 1)—are detected. At step 720, adifferential between operational and non-operational levels of one ormore signal characteristics may also be detected. For example, as shownin FIG. 5, the differential between the level of operational currentdetected at step 710 and the non-operational current level detected atstep 605 of FIG. 4 may be determined. Both the operational signalcharacteristic level(s) and the differential(s) of the attached surgicaldevice can be used to identify the manufacturer and/or part number ofthe attached surgical device.

At step 725, it is determined whether the detected operational signalcharacteristic level(s) and/or differential(s) are known, such that theyidentify a particular manufacturer and/or part number of the attachedsurgical device. If so, as shown at step 730, known optimalinflow/outflow rates for the attached surgical device may be set in thepump control circuit 120 (FIG. 1). If the detected values are notidentifiable, as shown at step 740, default inflow/outflow rates thatare generally compatible with most surgical devices may be set in thepump control circuit 120. (These default values may be automatically setin pump control circuit 120 prior to the determination in method 700; insuch a case, no change in the values is needed at step 740.) At step750, the method proceeds to step 620 of method 600 (FIG. 4).

FIGS. 6-8 depict different views of the exterior of the fluid managementsystem 100, in accordance with an exemplary embodiment of the invention.The exterior includes the inflow fluid pathway 410, outflow fluidpathways 420, and a display portion 430 for displaying flow rates andother operational parameters. The exterior also includes outflow door460 and cassette 470, described further below. Although not shown here,the exterior of the fluid management system 100 also includes power cord130 (see FIG. 1).

FIG. 7 shows, inter alia, a pinch mechanism 440 for switching betweenthe operational and non-operational outflow paths. Fluid managementsystem 100 may also include a pinch mechanism (not shown) for the inflowfluid pathway 410. Pinch mechanism 440 includes a wheel attached to arotating motor, such as a stepper motor.

It is often necessary to replace the tubes of the outflow pathway 420(i.e., the device and cannula tubes), due to the type of liquid beingdelivered or wear on the tubes. In the embodiment shown in FIG. 7, therotary motor of the pinch mechanism 440 moves to the center of its axisduring replacement of the outflow tubes. This feature eases setup of thefluid management system 100. While mechanisms of conventional fluidmanagement systems remain aligned to pinch off one of the outflow tubes,pinch mechanism 440 positions the wheel so as not to restrict any of theoutflow tubes. Pinch mechanism 440 can be configured to rotate to itscenter axis whenever the outflow door 460 is opened. A stepper motorprovides precise angular rotation to allow accurate positioning of thewheel.

Pinch mechanism 440 provides an advantageous configuration forinstalling and replacing the tubes of the outflow pathways 420. Becausepinch mechanism 440 frees all of the tubes of the outflow pathways 420during replacement of the outflow tubes (for example, when outflow door460 is opened), the user can attach or detach a cassette 470 thatcontains all outflow tubes, rather than threading individual tubes intofluid management system 100.

FIG. 9 illustrates a front view and a cross-sectional view of a cassette470 for use with fluid management system 100, in accordance with anexemplary embodiment of the invention. As shown in FIG. 9, cassette 470can include a sensible element 475. Sensible element 475 may be, forexample, a metal pin that can be detected magnetically. Alternatively,sensible element 475 may be a radio-frequency identification (RFID)device or other identifiable device that can be detected with radiowaves, infrared waves, or other known methods.

FIG. 10 illustrates an exploded rear view of a section of fluidmanagement system 100, in accordance with an exemplary embodiment of theinvention. As shown, fluid management system 100 includes cassettesensor 480, which may be mounted in place by a bracket 485. Cassettesensor 480 is configured to detect the presence of sensible element 475(FIG. 9), and may be a sensor configured to detect the presence ofmetal, or a frequency-sensitive device such as an RFID sensor.

Cassette sensor 480 can be used to authenticate cassettes used withfluid management system 100. Pump control circuit 120 can be used tomonitor a signal output by cassette sensor 480, and until cassettesensor 480 detects the presence of sensible element 475, pump controlcircuit 120 can be configured to enable or not perform the outflowoperations of fluid management system 100. Alternatively, pump controlcircuit 120 can be configured to disable both inflow and outflowoperations until the presence of sensible element 475 is detected. Inother words, if fluid management system 100 does not detect the presenceof the sensible element 475, the inflow/outflow pump will not run. Inaddition, the signal from cassette sensor 480 can be used to ensure thatthe cassette 470 is correctly loaded in place in fluid management system100 before allowing operation.

Fluid management system 100 can also be configured to estimate the fluidpressure at the operative site. For example, the pressure at the outputof the inflow path 210 (FIG. 6) can be measured and used to estimate thefluid pressure at the operative site using a pressure algorithm. Itshould be understood, however, that the embodiments described herein arenot limited to this method of estimation, and can be applied to anyknown process for estimating a pressure level.

Referring back to FIG. 3, pump control circuit 120 receives pressuredata at the pump controller 300 from a pressure sensor at the inflowpathway 210 of fluid management system 100 (FIG. 4). Conventionalestimation techniques assume that the pressure at the operative siteremains in a constant relationship (e.g., proportional) to the pressuremeasured at the inflow path 210. Thus, conventional estimationtechniques use a static technique, applying the same pressure algorithmduring both operational and non-operational states of the fluidmanagement system 100, and when differing flow rates are used.

As the flow rate increases, however, the relationship between the inflowpressure and actual pressure at the operative site does not remainconstant. Rather, the actual pressure increases non-linearly versus thedetected pressure as the flow rate of the inflow/outflow pump increases(such as when the surgical device is operational). Thus, it isbeneficial to adjust the pressure algorithm used to estimate thepressure at the operative site as the flow rate increases (i.e.,dynamically), and vice versa.

Dynamic calculation of the pressure at the operative site using realtime flow rates produces higher accuracy results. Applicants haveobserved that, when the system flow rate approaches zero, the measuredpressure at the pump approximately equals the pressure at the operativesite. As flow rate increases, however, the pressure at the operativesite is less than the measured pressure at an increasing rate. Thus,using such a dynamic method provides a better representation of theactual pressure at the operative site—i.e., the physiological jointpressures.

In one embodiment, when detection circuit 115 (FIG. 1) provides a signalto pump control circuit 120 indicating that the surgical device isoperational, in addition to changing other operational modes of fluidmanagement system 100, pump control circuit 120 can adjust the pressurealgorithm used to convert the received inflow pressure data to estimatedpressure data. The pressure algorithm may be adjusted for operationaland non-operational states and according to the flow rates of theseoperational and non-operational states.

FIG. 11 illustrates a flow diagram of a method 800 for adjusting apressure algorithm of a fluid path (which may be an inflow fluid path,outflow fluid path, or both) in a fluid management system, in accordancewith an exemplary embodiment of the invention. The method begins at step801, which may take place upon power-up of the fluid management system,or at any time after. At step 805, one or more signal characteristicsare detected, and at step 810 a determination is made whether theattached device is in an operational state, in accordance with methodsand apparatuses discussed above.

If the attached device is determined to be in an operational state, instep 820 pump controller 300 (FIG. 3) may detect (or read from memory)the operational flow rate of the fluid path. (Detection of the flow ratemay instead occur after adjusting the pressure algorithm betweenoperational and non-operational settings, or not at all.) In step 825,the pressure algorithm either remains or is adjusted to its operationalsettings. This may include adjusting variables or equations used tocalculate the estimated pressure value from the detected pressure value.

If instead the attached device is determined to be in a non-operationalstate, in step 830 pump control circuit 120 may detect thenon-operational flow rate, in similar manner to detection of theoperational flow rate, as discussed above. At step 835, the pressurealgorithm either remains or is adjusted to its non-operational settings.

After detecting the operational state of the attached device andadjusting the pressure algorithm accordingly, at step 840 the pressureof the fluid path is detected. At step 845, the pressure algorithm isapplied to the detected pressure to calculate an estimated pressure,representing the pressure at the operative site. At step 850, theestimated pressure is output, for example to display 430 (FIG. 6).

It should be understood that the pressure algorithm may be applied bypump controller 300 (FIG. 3), which may be a circuit such as amicro-controller, an ASIC, or a programmable integrated circuit. Thepressure algorithm may also be applied by another circuit in or externalto pump control circuit 120. The pressure algorithm may be implementedvia hardware or software, or a combination of both. In addition, itshould be understood that the above-described method of estimatingpressure is but one example of a method of estimating pressure at anoperative site using a pressure algorithm, and the adjustment of apressure algorithm according to operational states and/or flow rates isnot so limited to use with this method of estimating pressure. Further,method 800 may be applied for purposes of estimating pressure or othervariables at sites other than an operative site.

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications, embodiments andsubstitution of equivalents all fall within the scope of the invention.Accordingly, the invention is not to be considered as limited by theforegoing description, but only by the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A device for controlling a direction of a fluidpath of a fluid management system, said mechanism comprising: a rotatingmotor; a wheel attached to the rotating motor to restrict a first tubeof said fluid path when said rotating motor rotates to one of a firstand second position and a second tube of said fluid path when saidrotating motor rotates to the other of said first and second positions,wherein said rotating motor is configured to rotate to a third positionduring replacement of said first and second tubes; and a cassetteholding the first and second tubes, the cassette being attachable to anddetachable from the fluid management system, wherein the rotating motoris configured to rotate to a center of its axis during loading andunloading of the first and second tubes.
 2. The device of claim 1,wherein said rotating motor is a stepper motor.
 3. The device of claim1, wherein said rotating motor is a stepper motor and said thirdposition is the center of the rotating motor's axis.
 4. The device ofclaim 1, wherein said rotating motor is configured to rotate to saidthird position during attachment or detachment of said cassette.
 5. Thedevice of claim 1, said cassette further comprising a sensible elementdetectable by said fluid management system, wherein said fluidmanagement system is configured to not operate said fluid path unlesssaid sensible element is detected.
 6. The fluid management system ofclaim 5, wherein said sensible element is a metal pin.